.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\" and Copyright (C) 2011 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
.\" Distributed under GPL
.\" %%%LICENSE_END
.\"
.TH CATAN 3 2021-03-22 "" "Linux Programmer's Manual"
.SH NAME
catan, catanf, catanl \- complex arc tangents
.SH SYNOPSIS
.nf
.B #include <complex.h>
.PP
.BI "double complex catan(double complex " z );
.BI "float complex catanf(float complex " z );
.BI "long double complex catanl(long double complex " z );
.PP
Link with \fI\-lm\fP.
.fi
.SH DESCRIPTION
These functions calculate the complex arc tangent of
.IR z .
If \fIy\ =\ catan(z)\fP, then \fIz\ =\ ctan(y)\fP.
The real part of y is chosen in the interval [\-pi/2,pi/2].
.PP
One has:
.PP
.nf
    catan(z) = (clog(1 + i * z) \- clog(1 \- i * z)) / (2 * i)
.fi
.SH VERSIONS
These functions first appeared in glibc in version 2.1.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR catan (),
.BR catanf (),
.BR catanl ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
.SH EXAMPLES
.EX
/* Link with "\-lm" */

#include <complex.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>

int
main(int argc, char *argv[])
{
    double complex z, c, f;
    double complex i = I;

    if (argc != 3) {
        fprintf(stderr, "Usage: %s <real> <imag>\en", argv[0]);
        exit(EXIT_FAILURE);
    }

    z = atof(argv[1]) + atof(argv[2]) * I;

    c = catan(z);
    printf("catan() = %6.3f %6.3f*i\en", creal(c), cimag(c));

    f = (clog(1 + i * z) \- clog(1 \- i * z)) / (2 * i);
    printf("formula = %6.3f %6.3f*i\en", creal(f2), cimag(f2));

    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR ccos (3),
.BR clog (3),
.BR ctan (3),
.BR complex (7)
.SH COLOPHON
This page is part of release 5.13 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
